U.S. patent number 5,444,373 [Application Number 08/248,533] was granted by the patent office on 1995-08-22 for biomagnetometer with selectable pickup coil array.
This patent grant is currently assigned to Biomagnetic Technologies, Inc.. Invention is credited to Richard T. Johnson, Laurence Warden.
United States Patent |
5,444,373 |
Johnson , et al. |
August 22, 1995 |
Biomagnetometer with selectable pickup coil array
Abstract
A biomagnetometer comprises an array of biomagnetic sensors, the
array comprising a first plurality of magnetic field pickup coils,
and a second plurality of detectors, each of which receives a
pickup coil output from a pickup coil. There is a third plurality
of signal processors, each of which receives an output from a
detector, the third plurality of signal processors being fewer in
number than the first plurality of pickup coils. The
biomagnetometer further includes a selector that selects a subset
of pickup coils, equal in number to the third plurality of signal
processors, from the first plurality of pickup coils for signal
processing by the signal processors. This biomagnetometer permits
the placement of a very large array of relatively inexpensive
pickup coils adjacent to a subject, and then processing information
from subsets of that large array selected to optimize the gathering
of data, while maintaining the cost of the signal processing
electronics at a more economical level.
Inventors: |
Johnson; Richard T. (San Diego,
CA), Warden; Laurence (San Diego, CA) |
Assignee: |
Biomagnetic Technologies, Inc.
(San Diego, CA)
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Family
ID: |
25260159 |
Appl.
No.: |
08/248,533 |
Filed: |
May 23, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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831902 |
Feb 6, 1992 |
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Current U.S.
Class: |
324/248; 324/247;
340/870.31; 370/532; 600/409 |
Current CPC
Class: |
G01R
33/0354 (20130101); A61B 5/245 (20210101) |
Current International
Class: |
A61B
5/04 (20060101); G01R 33/035 (20060101); G01R
033/035 (); A61B 005/05 (); G08C 015/06 (); H04J
003/00 () |
Field of
Search: |
;324/242,243,244,247,248,260 ;128/653.1 ;370/112
;340/825.03,825.1,825.11,870.13 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0200080A1 |
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Dec 1986 |
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EP |
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0408302A3 |
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Jan 1991 |
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EP |
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Other References
Anon., "Squid Multiplexing Technique", IBM Technical Disclosure
Bulletin, vol. 29, No. 6, pp. 2434-2435 (Nov. 1986). .
Anon., "Squid Multiplexing Method", IBM Technical Disclosure
Bulletin, vol. 29, No. 6, p. 2513 (Nov. 1986). .
S. Erne et al., "The Positioning Problem in Biomagnetic
Measurements: A Solution for Arrays of Superconducting Sensors,"
IEEE Trans. on Magnetics, vol. MAG-23, No. 2, pp. 1319-1322 (Mar.
1987). .
H. E. Hoenig et al., "Biomagnetic multichannel system with
integrated Squids and first order gradiometers operating in a
shielded room," Cryogenics, vol. 29, pp. 809-813 (Aug. 1989). .
Jukka Knuutila, "Multi-Squid Magnetometers for Neuromagntic
Research," Cryogenics, vol. 30, pp. 1-8 (Sep. 1990)..
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Primary Examiner: Strecker; Gerard R.
Attorney, Agent or Firm: Garmong; Gregory
Parent Case Text
This application is a continuation of application Ser. No. 831,902,
filed Feb. 6, 1992, abandoned.
Claims
What is claimed is:
1. A biomagnetometer, comprising:
an array of biomagnetic sensors, the array comprising
a first plurality of magnetic field pickup coils, and
a second plurality of detectors, each of which is functional to
detect a pickup coil output, the second plurality of detectors
being fewer in number than the first plurality of pickup coils;
a third plurality of signal processors equal in number to the
second plurality of detectors, each of which signal processors is
functional to process an output of a single one of the second
plurality of detectors; and
means for controllably selecting a first selected subset of pickup
coils, equal in number to the third plurality of signal processors,
from the first plurality of pickup coils for signal processing by
the signal processors, and thereafter for controllably selecting a
second selected subset of pickup coils from the first plurality of
pickup coils for signal processing by the signal processors, equal
in number to the third plurality of signal processors, for signal
processing by the signal processors, the second subset of pickup
coils being different from the first subset of pickup coils, the
means for controllably selecting in each case being operable to
accomplish a connection of each one of the selected subset of
pickup coils to a respective one of the detectors, the means for
controllably selecting being operable to controllably connect any
of the pickup coils to any of the detectors.
2. The biomagnetometer of claim 1, wherein the means for selecting
includes switching means for connecting the outputs of the selected
subset of pickup coils to the second plurality of detectors.
3. The biomagnetometer of claim 1, wherein at least some of the
detectors are superconducting quantum interference devices.
4. The biomagnetometer of claim 1, further including means for
analyzing the output signals of an array of pickup coils.
5. The biomagnetometer of claim 1, further including a lead
extending between each of the magnetic field pickup coils and each
of the detectors, the lead being made of a material that becomes a
superconductor at a temperature below a superconducting
temperature, and wherein the means for selecting includes
a heater means associated with each of the pickup coils for
controllably heating the respective leads from a temperature below
the superconducting temperature to a temperature above the
superconducting temperature.
6. A biomagnetometer, comprising:
an array of biomagnetic sensors, the array comprising
a first plurality of magnetic field pickup coils, and
a second plurality of SQUID detectors equal in number to the first
plurality of magnetic field pickup coils, each of which receives a
pickup coil output from a single one of the pickup coils;
a third plurality of signal processors, the third plurality of
signal processors being fewer in number than the first plurality of
pickup coils and second plurality of SQUID detectors; and
switch means for switching an output of a respective one of each of
a subset composed of a third plurality of SQUID detectors, equal in
number to the third plurality of signal processors and selected
from the second plurality of SQUID detectors, to an input of a
respective single one of each of the third plurality of signal
processors, the switch means including means for selecting
different subsets of SQUID detectors for switching at different
times.
7. The biomagnetometer of claim 6, wherein the means for selecting
includes means for analyzing the output signals of an array of
pickup coils.
8. The biomagnetometer of claim 6, wherein the means for selecting
includes
a multiplexer.
9. The biomagnetometer of claim 6, further including
means for cooling the magnetic field pickup coils and the SQUID
detectors.
10. A biomagnetometer, comprising:
an array of biomagnetic sensors, the array comprising
a first plurality of magnetic field pickup coils, and
a second plurality of SQUID detectors, the second plurality of
SQUID detectors being fewer in number than the first plurality of
magnetic field pickup coils;
a third plurality of signal processors equal in number to the
second plurality of SQUID detectors, each of which signal
processors receives an output from a single SQUID detector; and
switch means for switching an output of a respective one of each of
a second plurality of pickup coils, equal in number to the second
plurality of SQUID detectors and selected from the first plurality
of magnetic field pickup coils, to an input of a respective single
one of each of the second plurality of SQUID detectors, the switch
means being operable to controllably connect any of the pickup
coils to any of the detectors.
11. The biomagnetometer of claim 10, further including means for
analyzing the output signals of an array of pickup coils.
12. The biomagnetometer of claim 10, further including
means for cooling the magnetic field pickup coils and the SQUID
detectors.
13. The biomagnetometer of claim 10, further including a lead
extending between each of the magnetic field pickup coils and each
of the detectors, the lead being made of a material that becomes a
superconductor at a temperature below a superconducting
temperature, and wherein the means for selecting includes
a heater means associated with each of the pickup coils for
controllably heating the respective leads from a temperature below
the superconducting temperature to a temperature above the
superconducting temperature.
14. A method for gathering biomagnetic information, comprising the
steps of
providing a biomagnetometer including
an array of biomagnetic sensors, the array comprising a first
plurality of magnetic field pickup coils, and a second plurality of
detectors, each of which detectors is a device whose function is to
detect a pickup coil output from a pickup coil, and
a third plurality of signal processors, each of which is a device
whose function is to process a detector output from a detector, the
third plurality of signal processors being fewer in number than the
first plurality of pickup coils;
controllably selecting a first subset of pickup coils, no greater
in number than the third plurality of signal processors, from the
first plurality of pickup coils for signal processing by the signal
processors, wherein any of the pickup coils may be selected for
processing by any of the detectors;
establishing electrical connection from each one of the selected
first subset of pickup coils, through a respective single one of
the detectors, and to a respective single one of the signal
processors; thereafter
controllably selecting a second subset of pickup coils different
from the first subset of pickup coils, no greater in number than
the third plurality of signal processors, from the first plurality
of pickup coils for signal processing by the signal processors,
wherein any of the pickup coils may be selected for processing by
any of the detectors; and
establishing electrical connection from each one of the selected
second subset of pickup coils, through a respective single one of
the detectors, and to a respective single one of the signal
processors.
15. The method of claim 14, including the additional steps, after
the step of establishing, of
selecting a second subset of pickup coils from the first plurality
of pickup coils for signal processing; and
establishing electrical connection from the selected second subset
of pickup coils, through a detector for each of the pickup coils,
and to the signal processors.
Description
BACKGROUND OF THE INVENTION
This invention relates to the measurement of the small magnetic
fields produced by the body of a living organism, and, more
particularly, to a biomagnetometer with a large array of pickup
coils.
The biomagnetometer is a device that measures the very small
magnetic fields produced by the body of a living organism. The
magnetic fields, particularly those produced by electrical currents
flowing in the brain and the heart, can be important indicators of
the health of the body, because aberrations in the magnetic field
can be associated with certain types of disfunctions either for
diagnosis or early prediction. Moreover, the magnetic fields
produced by the brain are an indicator of sensory, motor, or
thought processes and the location at which such processes occur,
and can be used to investigate the mechanisms of such
processes.
Magnetic fields produced by the body are very small, because they
result from very small electrical current flows. Typically, the
strength of the magnetic field produced by the brain is about
0.00000001 Gauss. By comparison, the strength of the earth's
magnetic field is about 0.5 Gauss, or over ten million times larger
than the magnetic field of the brain.
The biomagnetometer must therefore include a very sensitive sensor
of magnetic fields and sensor channels to process and analyze the
output signals of the sensors. Current biomagnetometers utilize a
sensor and sensor channel including a pickup coil which produces an
electrical current output when a magnetic field penetrates the
pickup coil. The electrical current, which is typically very small
in magnitude, is detected by a Superconducting QUantum Interference
Device, also known by the acronym SQUID. The pickup coil and SQUID
normally operate in a superconducting state at reduced temperature.
The output signal of the SQUID is provided to ambient-temperature
electronics that process and filter the output signal, and
thereafter the processed signal is analyzed to determine its
relation to the operation of the human body.
Spurious effects from the detection of other magnetic fields than
those produced by the brain can be removed by appropriate
electronic signal filters. However, the ability of filters to
remove all of the extraneous effects is limited. To further improve
the signal-to-noise ratio of the system, the subject and pickup
coil can be located in a magnetically shielded room.
Over the past 10 years, an important development in the field of
biomagnetometry has been an increase in the number of sensors and
sensor channels that are available on commercial units. That number
has increased from 1 to 7, then to 14 and currently to as many as
37 sensors and sensor channels in a single biomagnetometer. The
increase in the numbers of sensors is a highly desirable trend,
because the ability to relate the magnetic signals measured by the
sensors back to the functioning of the living organism can by
improved by the analysis of large arrays of sensor signals, as
discussed in U.S. Pat. No. 4,977,896.
As the number of sensors and sensor channels increases, the cost of
the biomagnetometer increases accordingly. Although economies of
scale and various manufacturing improvements have had some effect
on controlling the increase in system costs, in general the larger
biomagnetometer systems are much more expensive than the smaller
systems. It is likely that future systems with 100 or more sensors
and sensor channels will be even more expensive. The development of
the field of biomagnetometry and the subsequent availability of
this new tool to the general population may be inhibited by the
expected large increases in system costs.
There is an ongoing need for an approach to the construction of
very large sensor arrays without proportional increases in costs.
While improvements in design and manufacturing techniques are
helpful, they are not sufficient to reduce the projected systems
costs to the extent desired so that large-array biomagnetometers
will be priced for widespread use. The present invention fulfills
this need, and further provides related advantages.
SUMMARY OF THE INVENTION
The present invention provides a process for obtaining biomagnetic
data and a biomagnetometer for collecting magnetic data produced by
a living organism. The approach of the invention achieves data
acquisition with the power of a large sensor array at a fraction of
the cost normally required for such a large array. The accuracy of
data collection is greater than possible with conventional
equipment. Full-head coverage with a stationary array of sensors is
possible at a cost substantially less than if conventional methods
were used. The approach also permits general scanning of the
biomagnetic output of a portion of the body, and the subsequent
focussing of high-resolution data gathering on a region of
interest.
In accordance with the invention, a biomagnetometer comprises an
array of biomagnetic sensors. The array of sensors comprises a
first plurality of magnetic field pickup coils, and a second
plurality of detectors, each of which receives a pickup coil output
from a pickup coil. The biomagnetometer further includes a third
plurality of signal processors, each of which receives an output
from a detector, the third plurality of signal processors being
fewer in number than the first plurality of pickup coils. There is
means for selecting a subset of pickup coils, equal in number to
the third plurality of signal processors, from the first plurality
of pickup coils for signal processing by the signal processors.
The biomagnetometer has a greater number of pickup coils than
signal processors. In one preferred embodiment, there is a detector
for each pickup coil, in which case there is a switching capability
so that the signal processors may be connected to different subsets
of pickup coil/detector combinations. In another embodiment, there
is one detector for each signal processor, in which case there is a
switching capability so that the signal processor/detector
combinations may be connected to different subsets of pickup
coils.
In the preferred approach, the pickup coils are formed of one or
more turns of materials that are superconducting when cooled below
their superconducting transition temperatures. The pickup coils may
be wound in various geometric configurations such as magnetometers,
axial gradiometers, planar gradiometers, etc. The detectors are
preferably superconducting quantum interference devices (known in
the art as "SQUIDs") formed of materials that are superconducting
when cooled below their superconducting transition temperatures.
The signal processors are preferably ambient-temperature electronic
circuits, each of conventional design.
The present invention arises from the recognition of the fact that
the pickup coils are relatively inexpensive as compared with the
signal processors. It is the signal processors that add the
greatest cost, per added channel, of large-scale sensor arrays.
Each added channel also increases the volume of data that must be
processed and analyzed before a result can be displayed. The pickup
coils are readily fabricated as large arrays that can provide
full-area coverage of a part of the body, but it is comparatively
costly to provide a signal processor for each of the pickup coils
where the number of pickup coils becomes large. The SQUID detector
has an intermediate cost, but the selection of whether a SQUID is
provided for every pickup coil relates primarily to the
availability of suitable switches that are operable at cryogenic
temperature. At the present time switching capability is more
readily provided at ambient temperature. It is therefore preferred
to have one detector for each pickup coil, and to make the
switching between subsets of pickup coils/detectors using
ambient-temperature switches.
In accordance with a processing aspect of the invention, a method
for gathering biomagnetic information comprises the steps of
providing a biomagnetometer including an array of biomagnetic
sensors, the array comprising a first plurality of magnetic field
pickup coils, and a second plurality of detectors, each of which
receives a pickup coil output from a pickup coil, and a third
plurality of signal processors, each of which receives an output
from a detector, the third plurality of signal processors being
fewer in number than the first plurality of pickup coils. The
method further includes selecting a subset of pickup coils, no
greater in number than the third plurality of signal processors,
from the first plurality of pickup coils for signal processing by
the signal processors, and establishing electrical connection from
the selected subset of pickup coils, through a detector for each of
the pickup coils, and to the signal processors.
The method permits selective focussing of the biomagnetometer on
events of interest in the organism. After the initial steps, there
may be the additional steps of selecting a second subset of pickup
coils from the first plurality of pickup coils for signal
processing, and establishing electrical connection from the
selected second subset of pickup coils, through a detector for each
of the pickup coils, and to the signal processors. Thus, the first
subset of pickup coils can be those selected to provide coarsely
spaced, low-resolution coverage of a region of interest. Once an
event is detected with this large-area array, a second array
(usually with the same number of pickup coils) that covers a
smaller overall area is selected to provide higher spatial
resolution in that specific area. The advantages of both
large-area, low-resolution and small-area, high-resolution
biomagnetometry are thereby achieved with a single system that
costs only marginally more than conventional systems which cover
only a small area.
The present invention provides an important advance in the area of
biomagnetometry. It permits the number of sensors and sensor
channels to be increased to very large numbers while maintaining
the total system cost at a reasonable level. System performance is
also increased by reduced processing time. And, where
low-temperature pickup coil/SQUID switching is available, there is
greater cryogenic efficiency and operating costs since fewer
electrical leads are required from the interior of the dewar. Other
features and advantages of the invention will be apparent from the
following more detailed description of the preferred embodiments,
taken in conjunction with the accompanying drawings, which
illustrate, by way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic depiction of a biomagnetometer;
FIG. 2 is a block diagram of a single sensor channel;
FIG. 3 is a block diagram of one embodiment of the invention;
and
FIG. 4 is a block diagram of a second embodiment of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As illustrated in FIG. 1, the present invention is preferably
embodied in an apparatus 10 for obtaining biomagnetic data from the
body 12 of a human patient or subject. More specifically, the data
is normally obtained from biomagnetic sources within the head 14 of
the person. The person lies upon a table 16 (or sits on a chair) in
proximity to a biomagnetometer 18. The biomagnetometer 18 includes
a plurality of magnetic field pickup coils 20 for measuring small
magnetic fields. The pickup coils may be magnetometers or
gradiometers, or of other configuration as may be appropriate for a
particular application. In each operating sensor channel, the
output signal of the magnetic field pickup coil 20 is detected by a
detector, preferably a superconducting quantum interference device
21 (SQUID). Both the magnetic field pickup coil 20 and the SQUID 21
are maintained at a cryogenic operating temperature within a dewar
22. In the preferred practice a large number of sensing coils 20
and SQUIDs 21 are located in the dewar 22.
The electronics arrangement of the biomagnetometer 18 is
illustrated structurally in FIG. 1 and functionally for a single
complete sensor channel in FIG. 2. The magnetic signals from the
brain are picked up by the magnetic field pickup coil 20 in the
dewar 22, which produces a small electrical current output signal
when penetrated by a magnetic flux. The output signal of the pickup
coil 20 is detected by a detector, in this case the SQUID 21. The
SQUID 21 detects the magnetic field flux as an electrical current.
The output signal of the SQUID is processed in an
ambient-temperature signal processor 24 and stored in a computer 26
as a function of time.
The pickup coil 20 and the body 12 of the patient are preferably,
but not necessarily, enclosed within an enclosure 28 (also termed a
magnetically shielded room or MSR) that shields the apparatus and
magnetic field source from external influences. By screening off
the external influences, the amount of signal processing and
filtering required to obtain a meaningful indication of the
biomagnetic field is reduced.
Biomagnetometers of this general type are available commercially,
and their basic structure and operation are known. The operation of
SQUIDs and ambient-temperature SQUID electronics are disclosed in
U.S. Pat. Nos. 3,980,076; 4,079,730; 4,386,361; and 4,403,189. A
biomagnetometer is disclosed in U.S. Pat. No. 4,793,355.
Magnetically shielded rooms are disclosed in U.S. Pat. Nos.
3,557,777 and 5,043,529. A signal analysis procedure is disclosed
in U.S. Pat. No. 4,977,896. The disclosures of all of these patents
are incorporated herein by reference.
In the approach of the invention, there is a first plurality of the
pickup coils 20, a second plurality of the SQUIDs 21, and a third
plurality of the signal processors 24. The first plurality of
pickup coils 20 is larger in number than the third plurality of
signal processors 24. The second plurality of SQUIDs 21 may be
equal to the number of the first plurality of pickup coils 20 or to
the number of the third plurality of signal processors 24,
depending upon the system configuration. Two preferred system
configurations corresponding to these alternatives are illustrated
in FIGS. 3 and 4, respectively.
In accordance with one preferred embodiment, a biomagnetometer
comprises an array of biomagnetic sensors, the array comprising a
first plurality of magnetic field pickup coils, and a second
plurality of SQUID detectors equal in number to the first plurality
of magnetic field pickup coils, each of which receives a pickup
coil output from a pickup coil. There is further a third plurality
of signal processors, the third plurality of signal processors
being fewer in number than the first plurality of pickup coils and
the second plurality of SQUID detectors, and switch means for
switching the outputs of the second plurality of SQUID detectors to
the third plurality of signal processors.
FIG. 3 presents a block diagram for a biomagnetometer constructed
according to this approach. In the illustrated example, a first
plurality of pickup coils 32, 34, 36, 38, and 40 is five in number.
A second plurality of SQUID detectors 42, 44, 46, 48, and 50 is
also five in number. Each SQUID detector 42, 44, 46, 48, and 50
receives the output of a respective one of the pickup coils 32, 34,
36, 38, and 40. (Each pickup coil has two wires extending to it,
and each of the lines extending between a pickup coil and a SQUID
detector represents these two wires.) The pickup coils and SQUIDs
are located within an operable environment, typically a cryogenic
environment within the dewar 22.
A third plurality of signal processors 52, 54, and 56 is three in
number in this illustration, less than the first plurality of
pickup coils and the second plurality of SQUIDs. Each signal
processor 52, 54, and 56 receives the output of a multiplexer 58,
60, and 62, respectively. The signal processors and multiplexers
operate at ambient temperature.
The input of each multiplexer is connected so that it receives the
output of a number of SQUIDs. As shown in FIG. 3, the multiplexer
60 is connected so that it receives the output of each of the
SQUIDs 42, 44, 46, 48, and 50, and selectively connects one of
those outputs to its signal processor 54. (The multiplexers 58 and
62 are each similarly connected to each of the SQUIDs 42, 44, 46,
48, and 50, but the connection lines are shown in interrupted form
in FIG. 3 for the sake of clarity of illustration. These
multiplexers 58 and 62 operate in a similar manner to the
multiplexer 60.) Equivalently, the multiplexer 60 could be arranged
so that it received the outputs of some smaller subset of SQUIDs,
such as the SQUIDs 42, 44, 46, and 48, but not the SQUID 50.
Under control of the computer 26, the multiplexer 60 selects one of
the outputs of the SQUIDs 42, 44, 46, 48, or 50, and thence the
respective signal of the pickup coils connected to the SQUIDs, as
input to the signal processor 54. The multiplexers 58 and 62 select
the output of others of the SQUIDs for input to their respective
signal processors. The result is that the signal processors
controllably receive the input of any array of pickup coils at a
particular moment.
An example aids in illustrating the utility of this approach. If we
suppose that the pickup coils 32, 34, 36, 38, and 40 completely
surround the head 14 of the subject, then selection and monitoring
of the pickup coils 32, 36, and 40 give a general indication of the
presence and origin of a magnetic field signal from the brain. That
is, during initial "coarse scale" monitoring the signal processor
52 might process the output from the pickup coil 32, the signal
processor 54 might process the output from the pickup coil 36, and
the signal processor 56 might process the output from the pickup
coil 40.
Once a magnetic field of interest was identified, its character
could be evaluated in greater detail by selecting some other
combination of pickup coils that would give a more accurate picture
of the origin of the magnetic field. The multiplexers would be
switched to a combination of pickup coil inputs expected to give a
better data set for understanding that event. That is, during a
"fine scale" monitoring the multiplexer 58 might be switched so
that the output signal of the SQUID 46 is provided to the signal
processor 52, the multiplexer 60 might be switched so that the
output signal of the SQUID 48 is provided to the signal processor
54, and the multiplexer 62 might be switched so that the output
signal of the SQUID 50 is provided to the signal processor 56. In
this way, the fields monitored by the pickup coils 36, 38, and 40
could be analyzed, assuming that these three pickup coils are
better located to provide information on the character of the event
under study in the brain.
This approach is ideally suited to select those arrays of pickup
coil signals that can provide the most information, highest
resolution, and best signal-to-noise ratio for monitoring
particular events. This information is used by array-processing
techniques such as that of U.S. Pat. No. 4,977,896. These
array-processing techniques are also desirably used in real time to
select the combination of pickup coils that provide the best
information on the event.
The ability to monitor the living organism over a wide area and
then selectively focus on a small area are achieved with a smaller
number of signal processors than the number of pickup coils. In the
example, there were only five pickup coils and three signal
processors. In a commercial unit, it is expected that there would
be on the order of at least several hundred pickup coils and fifty
or more signal processors. The ratio of pickup coils to signal
processors is also expected to be larger in commercial units. That
is, there might be a ratio of pickup coils to signal processors of
5:1 or 10:1 in such a commercial unit.
Another embodiment is illustrated in FIG. 4. In this case, there is
a first plurality of pickup coils 70, 72, 74, 76, and 78, again
five in number in the example. The output of each of the pickup
coils is connected to the input of each of a second plurality of
SQUIDs 80, 82, and 84, here three in number. The output of each of
the SQUIDs 80, 82, and 84 is connected to the input of one
respective third plurality of signal processors 86, 88, and 90,
here three in number.
Each of the output lines from the pickup coils 70, 72, 74, 76, and
78 to the inputs of the SQUIDs 80, 82, and 84 has a switch 92
therein. The switches 92 interrupt the signal transmission from any
pickup coil to any of the SQUIDs. (is in FIG. 3, each line from the
pickup coil represents two wires.) The number of switches 92 in
this example having a small number of coils is the product of the
first plurality times the second plurality, or 15 switches in the
illustrated example.
In a preferred approach wherein the pickup coils, SQUIDs, and
transmission lines therebetween are operated in the superconducting
state, the switches 92 are small heaters that are activated under
control of the computer 26. When a heater on a particular line is
activated, that line from the pickup coil to SQUID is driven normal
(i.e., not superconducting) so that no current passes through the
line, effectively opening the switch. With this approach,
particular subsets of pickup coils are connected to the SQUIDs 80,
82, and 84. The same types of "coarse scale" and "fine scale"
focusing discussed in relation to FIG. 3 are therefore possible
with this embodiment.
The difference between the approaches of FIGS. 3 and 4 is that the
switching occurs in normal metal lines in the arrangement of FIG. 3
and in superconducting lines in the arrangement of FIG. 4. The
latter is more difficult and less cryogenically efficient, but may
be preferred in particular circumstances. Selection of one approach
or the other will depend upon details of system design. For
example, the approach of FIG. 3 requires that more heat-conducting
electrical transmission lines extend from the interior of the dewar
to the exterior, but the approach of FIG. 4 requires heat input
into the switches 92.
The present invention provides an important advance in the field of
biomagnetometry. Large arrays of relatively inexpensive pickup
coils can be provided, together with smaller numbers of relatively
expensive signal processors. Subsets of the large number of pickup
coils are selected to meet varying requirements during coarsely and
finely focussed analyses of the organism. Although particular
embodiments of the invention have been described in detail for
purposes of illustration, various modifications may be made without
departing from the spirit and scope of the invention. Accordingly,
the invention is not to be limited except as by the appended
claims.
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